As for scavenged parts, you're going to need a warehouse of manuals and datasheets, eh?
Depending on the details of your post-apocalyptic scenario planning, simple automation driven by relays or clockwork logic will be more likely than e.g. scavenged microcontrollers.
I applaud the spirit of the project though: I don't want to live on Gilligan's Island making everything out of coconuts and vines.
You're right! As a thought experiment, let's say I download CollapseOS and then switch off my internet.
I have in my house a normal complement of electronic devices. I have a soldering iron, some wire etc. I assume if I start taking things apart I'll find some Z80s. Those Z80s will be living on boards with clock chips and memory etc. Where do I even start?